1. Field of the Invention
This invention relates generally to electromagnetic signal receiving devices, and more particularly to a multi-feed signal receiving device having a plurality of waveguide assembly and circuit layers for processing microwave signals.
2. Description of the Prior Art
Direct Broadcast Satellite (DBS) is a point-to-multipoint system in which individual households equipped with a small receiving antenna and tuner device receive broadcasts directly from a geostationary satellite. The satellite receives digital audio and video transmissions from ground stations and relays them directly to individuals. The receiving antenna is comprised of a parabolic dish designed to collect the satellite signals and focus them at the focal point, where an LNBF (Low Noise Block with integrated Feed) module is mounted to convert the incoming signals to a lower frequency band and transmit it to a tuner device. The LNBF module also acts as a filter and an amplifier-to selectively boost the signal received by the dish collector. The LNBF module comprises a feed for receiving microwave signals and circuitry for processing the received microwaves.
FIG. 1 shows the various parts of a prior art single-feed LNBF module. The LNBF module comprises a signal feed, a cylindrical waveguide, a signal processing module, and an output connector. Microwave signals are received by the signal feed and transmitted to the signal processing module through the waveguide. A cap is mounted in front of the signal feed to provide protection from dust and rain. The signal processing module is enclosed in a housing, and comprises probe pins coupled the waveguide energy to a printed circuit board. One typical probe pin structure is an L-type probe pin. A round opening is provided on the front end of the housing to allow microwave signals in the cylindrical waveguide to be coupled to the L-type probe pin.
The L-type probe pin couples the microwave signals to a processing circuitry on the printed circuit board. A spacer is provided at the back end of the printed circuit board to provide signal isolation and electric shielding. Typically, the processing circuitry provides amplification and frequency conversion functions. The microwave signals are converted to an intermediate frequency suitable for propagation in transmission cables. An output connector couples the amplified and frequency-converted signals to a transmission cable. The signals are then transmitted to a set top box or a signal decoder for further processing.
Normally, each satellite dish antenna is aligned to receive signals from a particular cluster (or group) of satellites in a certain direction. Microwave signals aligned to the axis of the parabolic antenna dish are collected at the focal point, where the LNBF module is located. When receiving signals from different satellite clusters, multi-feed LNBF modules are used. The multiple feeds of the LNBF module are placed closely together, and configured to allow signals from each satellite to be collected by the dish collector to the corresponding feeds. The signals are amplified and demodulated on a circuit board having microstrip lines and various electronic components. Because it is difficult to integrate electronic components in a single circuit board for different frequency bands and provide for different signal processing and prevent interference, a plurality of LNBF modules are used to process the signals individually. These LNBF modules are placed side-by-side, and a number of waveguides are required to guide the microwave signals from the signal feeds to the disparate LNBF modules. Such a configuration results in a large, complex, and expensive apparatus.